PURPOSE: To secure the data saving time by reducing the operation clock frequency of an LSI to suppress the temperature rise of the LSI for a certain time at the time of the abnormal rise of the temperature of the LSI.

CONSTITUTION: Though a device is cooled by an exhaust fan 3, an LSI 1 has a large power consumption and the exhaust fan 3 is short of air for the LSI 1; and therefore, it is partially cooled by a cooling fan 2 to supply the shortage. If the cooling fan 2 is abnormally stopped or is rotated at an abnormally low speed or the temperature of intake air is abnormally high, the LSI 1 is thermally destroyed by the temperature rise due to lack of cooling. If the temperature of intake air exceeds a limit value in another case, the LSI is thermally destroyed by the temperature rise. When these abnormalities occur and the abnormality report from an intake air monitor part 5, a fan monitor part 6, or an LSI temperature monitor part 7 is received by a clock varying part 4, the frequency of the operating clock of the LSI is reduced.